1. Field of the Invention
The present invention relates to a direction control valve, and more particularly to a direction control valve equipped with a valve body, which is formed with first and second communication switching ports and a communication object port, and a movable member axially moving inside the valve body to switch a port communicating with the communication object port between the first communication switching port and the second communication switching port.
2. Description of Related Art
FIG. 13 illustrates an example structure of this type of direction control valve. The direction control valve shown in FIG. 13 is a three-way valve having a valve body 110 and a movable member 112. The valve body 110 is formed with communication switching ports 110a, 110b and a communication object port 110c. The movable member 112 moves in the valve body 110 in a direction parallel to a axis 116 (in axial direction) of the valve body 110 to switch a port communicating with the communication object port 110c between the communication switching ports 110a, 110b. A hydraulic oil pressure PL is supplied to the communication switching port 110a, and a hydraulic oil pressure Pc is supplied to the communication switching port 110b. The communication object port 110c is connected to a switch chamber (S.C., not shown). In this example, the pressure Pc supplied to the communication switching port 110b is set higher than the pressure PL supplied to the communication switching port 110a. A control chamber 118 is defined by an inner peripheral surface of the valve body 110 and an end face of the movable member 112 opposite from the communication switching port 110b with respect to the axial direction. The hydraulic oil pressure supplied to the control chamber 118 produces a thrust acting on the movable member 112 toward the communication switching port 110b in the axial direction. The pressure in the control chamber 118 is controlled by opening and closing operation of a pilot valve 120. A spring 126 applies a biasing force to the movable member 112 in the axial direction away from the communication switching port 110b. Hereinafter, the axial direction away from the communication switching port 110b will be referred to as a first axial direction and the axial direction opposite to the first axial direction will be referred to as a second axial direction.
When the pilot valve 120 is closed, the pressure in the control chamber 118 pushes the movable member 112 in the second axial direction, so the movable member 112 closely contacts a seat 110d formed on the inner peripheral surface of the valve body 110. Thus, communication between the communication switching port 110b and the communication object port 110c is provided and communication between the communication switching port 110a and the communication object port 110c is broken, so the resulting pressure in the switch chamber is the pressure Pc. Then, if the pilot valve 120 is opened, the pressure in the control chamber 118 is reduced, so the movable member 112 separates from the seat 110d and moves in the first axial direction due to the biasing force of the spring 126. As a result, communication between the communication switching port 110a and the communication object port 110c is provided. Then, the movable member 112 closely contacts a seat 110e formed on the inner peripheral surface of the valve body 110, so the communication between the communication switching port 110b and the communication object port 110c is broken. In this manner, the pilot valve 120 is switched from the closed state to the opened state, thereby switching the port communicating with the communication object port 110c from the communication switching port 110b to the communication switching port 110a. As a result, the pressure in the switch chamber reduces from the pressure Pc to the pressure PL.
Then, if the pilot valve 120 is closed, the pressure in the control chamber 118 increases. Accordingly, the movable member 112 separates from the seat 110e and moves in the second axial direction due to the pressure in the control chamber 118. Thus, communication between the communication switching port 110b and the communication object port 110c is provided. Then, if the movable member 112 closely contacts the seat 110d formed on the inner peripheral surface of the valve body 110, the communication between the communication switching port 110a and the communication object port 110c is broken. In this manner, the pilot valve 120 is switched from the opened state to the closed state, thereby switching the port communicating with the communication object port 110c from the communication switching port 110a to the communication switching port 110b. As a result, the pressure in the switch chamber increases from the pressure PL to the pressure Pc. This type of direction control valve is also described in JP-A-2002-227747.
As another background technology, a fuel injection device is described in DE-A-10229419, JP-A-2002-539372, JP-A-2001-90634, or JP-A-2005-500472.
In the direction control valve shown in FIG. 13, there exists a period in which both the communication switching ports 110a, 110b communicate with the communication object port 110c when the port communicating with the communication object port 110c is switched. For example, in the stroke in which the movable member 112 moves in the second axial direction to switch the port communicating with the communication object port 110c from the communication switching port 110a to the communication switching port 110b, the movable member 112 separates from the seat 110e and then closely contacts the seat 110d. Thus, as shown in FIG. 14, both of the communication switching ports 110a, 110b communicate with the communication object port 110c during the period since the movable member 112 separates from the seat 110e until the movable member 112 closely contacts the seat 110d. In consequence, the hydraulic oil supplied to the high-pressure communication switching port 110b flows into the low-pressure communication switching port 110a, resulting in an increase in energy loss of the hydraulic oil.
Likewise, in the stroke in which the movable member 112 moves in the first axial direction to switch the port communicating with the communication object port 110c from the communication switching port 110b to the communication switching port 110a, both of the communication switching ports 110a, 110b communicate with the communication object port 110c during a period since the movable member 112 separates from the seat 110d until the movable member 112 closely contacts the seat 110e. The hydraulic oil supplied to the high-pressure communication switching port 110b flows into the low-pressure communication switching port 110a when the port communicating with the communication object port 110c is switched. In consequence, the energy loss of the hydraulic oil increases.